SOLUTION: The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 16 HCF of water is $34.60, and the

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 16 HCF of water is $34.60, and the      Log On


   

Question 1152386: The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 16 HCF of water is $34.60, and the cost for using 30 HCF is $57.70. What is the cost for using 28 HCF of water?

Answer by MathLover1(20850) About Me  (Show Source):
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given:
The monthly cost (in dollars) of water use is a linear function:
y=mx%2Bb where x represents HCF and y represents the cost for using
if the cost for using x=16 HCF of water is $y=34.60, means
that is a point (16,34.60)
the cost for using x=30 HCF is $y=57.70, means
that is a point (30,57.70)
use points to find slope m
m=%2857.70-34.60%29%2F%2830-16%29=23.1%2F14=1.65
=>y=1.65x%2Bb
to find b, use one point above
34.60=1.65%2A16x%2Bb
34.60=26.4x%2Bb
34.60-26.4x=b
b=8.20
and, your equation is: y=1.65x%2B8.20
use equation to calculate what is the cost for using x=28 HCF of water is:
y=1.65%2A28%2B8.20
y=46.20%2B8.20
y=54.40
the cost for using 28 HCF of water is 54.40